1. Paeoniaceae Rafinesque
Perennial herbs [shrubs], glabrous or hairy. Stems simple or branched, [± fleshy], ± scaly proximal to leaves proper; scales ± clasping, ± membranous. Leaves cauline, alternate, pinnately to ternately or biternately compound or divided; stipules absent; petiole present; blade sometimes ± leathery, ultimate margins entire or ± toothed. Inflorescences usually terminal, solitary flowers [2-3+ flowers in clusters]. Flowers bisexual; perianth and androecium perigynous; hypanthium absent; sepals [2-]5-6[-10+], distinct, unequal, ± leathery; petals [4-]5-6[-10+; -25+ in cultivars], distinct; stamens usually 50-200+, inserted on torus (sometimes called disc) interior to petals, distinct; anthers erect, basifixed, extrorse, dehiscent by longitudinal slits; staminodes absent, intrastaminal glands sometimes interpreted as staminodes; pistils [1-]5[-15], each 1-carpellate; ovary superior, distinct, 1-locular; placentation marginal; ovules anatropous, bitegmic, crassinucellate; styles 1 per carpel or ± absent; stigmas 1 per carpel, ± apical and adaxial. Fruits follicles, dehiscence adaxial. Seeds mostly 2-5 per carpel, dark brown to blackish, ± cylindric to arcuate [globose], outer integuments relatively thick, sometimes interpreted as arils; embryo dicotyledonous, relatively small; endosperm oily.
Genus 1, species ca. 30 (2 in the flora): w United States, nw Mexico, Eurasia.
Paeonia was long included in Ranunculaceae or was associated with Dilleniaceae. Angiosperm Phylogeny Group (2003) placed Paeoniaceae in Saxifragales.